As is known in the art, single-sided nuclear magnetic resonance (“NMR”) has the potential for use in a wide variety of different applications. For example, single-sided NMR sensors may find use as a portable diagnostic for disorders in fluid regulation. Such sensors require a remote, uniform magnetic field to achieve sufficient sensitivity.
Maintenance of fluid balance in the body is critical to physical and cognitive function yet no accurate, robust, and practical assessment method currently exists. Proper fluid management is necessary for renal and heart failure patients, competitive athletes, soldiers, and the elderly. Current approaches rely on indirect measures that are subject to significant variability during physician interpretation or invasive measures that cannot be routinely performed. These methods include blood and urine chemistry, bioimpedance, and even radioisotope dilution. All are either invasive, require a lab, or have proven to be not clinically reliable. Thousands of medical errors and billions of dollars of unnecessary expenditure occur annually due to improper fluid management in the US.
Proton nuclear magnetic resonance (1H NMR) relaxometry provides a direct measure of water volumes and concentration. The nucleic specificity of MR intrinsically measures only signal from water, which vastly improves sensitivity compared to other, easily confounded diagnostic methods. Magnetic resonance imaging (MRI), a specialized form of NMR, can measure fluid levels, but is highly impractical for routine diagnostic use due to extended measurement times, high cost, and limited availability.
Measurement of the fluid distribution in lean muscle tissue offers potential in managing fluid disorders such as dehydration and volume overload. However, accessing this tissue for measurement requires that the measurement penetrate beneath superficial tissue layers—such as, for example, the epidermis, dermis, or subcutaneous tissue layers. The ability of single-sided NMR systems to interrogate tissue remote to the surface of the sensor enables measurements of anatomical regions previously not possible with closed bore systems. Single-sided NMR relies on the existence of a remote uniform magnetic field. Ideally, the field lines of the homogenous region are parallel to the surface of the magnet to allow for the use of standard surface coils for radio frequency (RF) excitation and signal acquisition. A magnetic field with a large, high field strength uniform region is required for high sensitivity measurements.
It would, therefore, be desirable to provide a magnet geometry capable of providing a magnetic field having a high field strength and which is relatively homogeneous over a large region.